全文获取类型
收费全文 | 13571篇 |
免费 | 2517篇 |
国内免费 | 2002篇 |
专业分类
化学 | 9608篇 |
晶体学 | 225篇 |
力学 | 781篇 |
综合类 | 131篇 |
数学 | 1496篇 |
物理学 | 5849篇 |
出版年
2024年 | 28篇 |
2023年 | 235篇 |
2022年 | 402篇 |
2021年 | 508篇 |
2020年 | 586篇 |
2019年 | 504篇 |
2018年 | 493篇 |
2017年 | 474篇 |
2016年 | 682篇 |
2015年 | 693篇 |
2014年 | 887篇 |
2013年 | 1068篇 |
2012年 | 1166篇 |
2011年 | 1315篇 |
2010年 | 959篇 |
2009年 | 904篇 |
2008年 | 1013篇 |
2007年 | 945篇 |
2006年 | 856篇 |
2005年 | 695篇 |
2004年 | 531篇 |
2003年 | 431篇 |
2002年 | 454篇 |
2001年 | 398篇 |
2000年 | 291篇 |
1999年 | 283篇 |
1998年 | 209篇 |
1997年 | 189篇 |
1996年 | 182篇 |
1995年 | 126篇 |
1994年 | 86篇 |
1993年 | 92篇 |
1992年 | 69篇 |
1991年 | 81篇 |
1990年 | 52篇 |
1989年 | 39篇 |
1988年 | 31篇 |
1987年 | 29篇 |
1986年 | 31篇 |
1985年 | 28篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1976年 | 1篇 |
1971年 | 1篇 |
1957年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
Repeated irradiation enhances the precision and sensitivity of INAA based on short-live radionuclides, but entail systematic losses due to dead time. The relative standard deviation in the net peak area decreases with the square root of the number of cycles while the systematic bias increases with it. The limits of decision, detection and determination decrease in a somewhat more complicated way with the number of cycles. The derived formulation is applied to the determination of selenium in hair by the 161.9 keV photopeak of77mSe,T
1/2=17.8 s. 相似文献
133.
JunZhou Yong-zhiQiu Xiao-pengZang Chang-wangPan QiangChen JianShen Si-congLin 《高分子科学》2005,(1):93-102
N,N-dimethyl-N-methacryloyloxyethyl-N-carboxyethyl ammonium (DMMCA) was graft-copolymerized onto the surface of segmented poly(ether urethane) (SPEU) and PE film. The carboxybetaine structure on SPEU and PE film surfaces was confirmed by ATR-FTIR, XPS and water contact angle measurements. Through the experiments with platelet adhesion and protein adhesion assay in vitro, the two materials studied, including poly-DMMCA gel, all show excellent nonthrombogenicity. This confirms once again that the zwitterionic molecular structure on the surfaces of materials is essential for improving their nonthrombogenicity and biocompatibility. 相似文献
134.
Wu J Huang J Xiao Q Zhang S Xiao Z Li Q Long L Huang L 《Magnetic resonance in chemistry : MRC》2004,42(7):659-662
Ten phenylethanoid glycosides, including two new ones, isolated from the aerial parts of the mangrove plant Acanthus ilicifolius were identified. The first complete assignments of the 1H and 13C NMR chemical shifts for these glycosides were achieved by means of 2D NMR techniques, including 1H-1H COSY, TOCSY, HSQC and HMBC spectra. 相似文献
135.
二苄亚砜硝酸钕Nd(NO_3)_3·[(C_6H_5CH_2)_2S0]属三斜晶系,P1空间群,晶胞参数:a=9.835(2),b=12.445(2),c=19.971(5)A,α=104.13(2)°,β=90.34(2)°γ=74.96(1)°Z=2。晶体结构用重原子法解出,经最小二乘修正后R因子为0.031。钕离子由九个氧配位,形成稍歪扭的三帽三方棱柱配位多面体,其中一个三角面由三个二苄亚砜(DBSO)提供的氧形成,其他氧原子则由硝酸根提供。平均Nd-O(DBSO)=2.379A,Nd-O(NO_3)=2.536A。 相似文献
136.
Nishiura M Hou Z Wakatsuki Y Yamaki T Miyamoto T 《Journal of the American Chemical Society》2003,125(5):1184-1185
Various terminal alkynes have been cleanly dimerized into the corresponding head-to-head (Z)-enynes by use of the half-metallocene lutetium alkyl complexes Me2Si(C5Me4)(NAr)Lu(CH2SiMe3)(THF) (Ar = Ph, C6H3Me2-2,6, C6H2Me3-2,4,6) as catalysts. Aromatic C-Cl, C-Br, and C-I bonds, which are known to be extremely susceptible to reductive cleavage by transition metals, survived in the present reactions. The corresponding dimeric alkynide species [Me2Si(C5Me4)(NAr)Lu(mu-CCR)]2 are thought to be the true catalysts, some of which have been isolated and structurally characterized. These alkynide species were thermally stable and soluble at the reaction temperatures (80-110 degrees C), but they precipitated upon cooling to room temperature after completion of the reaction. Therefore, this catalyst system works homogeneously but can be separated and reused, thus constituting the first example of a recyclable catalyst system for the dimerization of terminal alkynes and also the first example of (Z)-selective head-to-head dimerization of aromatic terminal alkynes. 相似文献
137.
用比较力场分析研究了N-亚硝基化合物的结构与致癌活性的关系,考察了网络结构和探针原子对结果的影响.结果表明,立体效应和静电作用场是描述其致癌活性和进行结构性能关系研究的最重要的结构参数。 相似文献
138.
139.
The nonlinear optical membrane used for image processing was prepared using tetraethyl silicate by sol-gel method under mild conditions. Ru(bpy)3Cl2 (bpy, bipyridine) was immobilized in the sol-gel matrix. This light-excitable membrane containing Ru(bpy)3Cl2 as photocatalyst could catalyze the Belousov-Zhabotinsky reaction by illumination. Our results indicated that a fine-definition image processing could be autoperformed when projecting a picture on this medium. The imaging process was an image evolution process, which was similar to that of the human vision process. 相似文献
140.